linux-kernel - Re: [PATCH 1/2] sched/idle: Fix arch_cpu

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Date:   Tue, 1 Dec 2020 12:02:09 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     rafael@...nel.org, viresh.kumar@...aro.org, mingo@...nel.org,
        x86@...nel.org, mark.rutland@....com, will@...nel.org,
        svens@...ux.ibm.com, linux-kernel@...r.kernel.org,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH 1/2] sched/idle: Fix arch_cpu_idle() vs tracing

On Mon, Nov 30, 2020 at 01:00:03PM -0800, Guenter Roeck wrote:
> On Fri, Nov 20, 2020 at 12:41:46PM +0100, Peter Zijlstra wrote:
> > We call arch_cpu_idle() with RCU disabled, but then use
> > local_irq_{en,dis}able(), which invokes tracing, which relies on RCU.
> > 
> > Switch all arch_cpu_idle() implementations to use
> > raw_local_irq_{en,dis}able() and carefully manage the
> > lockdep,rcu,tracing state like we do in entry.
> > 
> > (XXX: we really should change arch_cpu_idle() to not return with
> > interrupts enabled)
> > 
> 
> Has this patch been tested on s390 ? Reason for asking is that it causes
> all my s390 emulations to crash. Reverting it fixes the problem.

My understanding is that it changes the error on s390. Previously it
would complain about the local_irq_enable() in arch_cpu_idle(), now it
complains when taking an interrupt during idle.